There are a variety of futon frames currently available that serve the dual function of providing a frame for a sofa and a bed. Many of these frames employ guide posts mounted on the back of the sofa which ride in guide slots in the base of the sofa. The guide posts, directed by the slots, assist in directing the back from an upright position to a horizontal position.
U.S. Pat. No. 3,107,364 is an early patent which employs a slot in combination with springs to facilitate the raising and lowering of a back element of a sofa. The frame, in addition to employing springs, requires additional hardware to provide the action required to convert the sofa to a bed.
U.S. Pat. No. 3,634,893 provides a sofa having either a two section bed surface (bi-fold sofa) or a three section bed surface (tri-fold sofa). Both types of frames have horizontal slots which assist in the raising and lowering of the sofa and do not require the use of a spring as part of the mechanism. However, the sofa of the '893 patent, while overcoming the need for springs, still requires extensive hardware to perform the desired function and, in addition, uses sectional cushions attached to the frame to form the bed surface.
U.S. Pat. No. 4,642,823 offers an improvement over the '364 patent and the '893 patent by reducing the hardware required by these earlier cited patents. However, in order to avoid flexing of the back and seat elements when the sofa is opened to form a bed, locking pins are required which can be extended into the back. Furthermore, when the back is in the upright position and the frame serves as a sofa, there is no locking mechanism to assure that the sofa will not inadvertently slip, reverting to a bed, if a substantial load is placed on the back. The only resistance to a load being placed on the back is the friction in the mechanisms, the weight of the back and seat of the frame, and the weight of the futon resting thereon.
U.S. Pat. No. 4,996,730 is similar to the '823 patent, however, does not provide the pins for locking the seat with respect to the back.
U.S. Pat. No. 4,875,244 has overcome the problem of the sofa inadvertently opening to form a bed even if a substantial pressure is applied to the back. The seat lockably engages the base of the sofa. However, this frame does not provide the locking mechanism provided by the '823 patent to assure that the back and seat will not flex when the seat and the back are aligned to form a bed.
The problem of providing a frame which will not inadvertently open or which will not flex when the seat and the back are aligned to form a base for an extended futon has been solved by the inventor of the present application in his earlier patent, U.S. Pat. No. 5,083,333 wherein he teaches the use of pins which are selectively engaged with slots of the sofa, locking the back with respect to the seat.
U.S. Pat. No. 5,153,951 also employs pins which engage slots to stabilize the back relative to the seat. However, the shape and configuration of the slots of the '951 patent would provide for less positive stabilization of the back in the upright position than the shape and configuration of the slots of the '333 patent.
While the mechanisms taught in the '333 patent and the '951 patent lock the seat with respect to the back, additional mechanisms are required if the seat and back are to be stabilized with respect to the frame. Without such stabilization, the back can overshoot to an upright position, resulting in high loads and torques on the frame. Sofas employing the hinge of the '333 patent as well as the sofas of the '244 patent, the '823 patent, and the '730 patent can be stabilized by having the ends of the guide slots positioned to serve as a stop to avoid overshooting of the back. However, if the ends of the slots are not properly aligned, since there is at best line contact, twisting of the seat and back with respect to the frame can occur. The twisting can interfere with the smooth action of the raising and lowering of the back.
Furthermore, there is no teaching in the '823, '244, '730, '333, or the '951 patents which would suggest a tri-fold sofa, let alone one that would couple the movement of a rear deck panel to the movement of the back. When the sofa is a tri-fold, the problem of twisting of the back with respect to the base can create additional problems by off setting the rear deck panel which, when coupled to the base, can result in additional torsional load. These loads can further interfere with raising or lowering the back to convert the sofa to a bed.
Thus, there is a need for a sofa/chair frame that will provide improved stability of the seat and back with respect to the frame and for a tri-fold sofa or chair that can be readily opened from the front in a single operation.